1. Field of the Invention
The present invention relates to a measuring system using laser technique for three-dimensional objects and complex surfaces. According to the invention, three-dimensional objects are preferably interior rooms in buildings with central stairwells and corridors, i.e. all interior rooms from basements to attics. Geological hollows with complex surfaces shall be cited as further examples whose surveying is possible with the novel measuring system using laser technique.
2. The Prior Art
For the professional groups architecture, building trade, expert consultants and restorers but also surveying firms, geologists and archaeologists the manual measuring out of existing interior spaces (the so-called "measuring up") or natural hollows is a frequently occurring and often rather complicated working process which entails considerable time and personnel efforts. In addition the "human" factor brings about errors and measuring inaccuracies that can only be corrected by repeated measuring. It can be stated in this context that the commonly used procedure, in which only an insufficient number of measuring points are determined manually, makes further inaccuracies in the sense of a true representation of deformation unavoidable.
It is a known fact that surveying of buildings has been conducted by means of photogrammetry for years. The following facts shall be stated regarding the above method:
The evaluation of the measurements which are available as digitised photos has only been partially automated to date, while essentially the recognition and determination of the object boundaries (i.e. visible edges and valleys) is done manually. PA1 It is due to the limited aperture angle and/or the strong boundary distortions in case of large aperture angles ("fisheye") that nearly exclusively facades or architectural details are measured. PA1 The high manual efforts and the pertaining costs are very high. In addition, the currently available measuring methods only allow for the determination of max. 3,000 measuring points per working day.
One measuring method in which laser technique is adopted is the pulse operation time method in which an extremely short light-induced pulse is emitted from a laser source and deflected via a mirror which rotates at a high angular speed. Said light-induced pulses are reflected by an object to be measured that is located at a max. distance of 50 m and recorded by an existing receiver in a laser scanner. The period of time between the emitting and receiving is measured and thus the distance to the scanned measuring object is determined for each ray and for each point on the scanned surface. This measuring method by means of a singular light-induced pulse from a transmitter to a measuring point and back to a receiver is called "pulse operation time method".
In this connection it is referred to DE 43 40 756 A 1, titled "Distance measurement using lasers". A laser radar is equipped with a pulsed laser, that emits controlled light-induced pulses into a measuring range, a photo receiver arrangement, which receives the light-induced pulses that are reflected by an object located in the measuring range, and an evaluation circuit which, under consideration of the velocity of light, uses the time period between the emission and reception of a light-induced pulse to determine a distance signal which is characteristic for the distance of the object. A light deflecting arrangement is positioned between the measuring range and the pulsed laser, said arrangement guides the light-induced pulses into the measuring range under increasingly modifying angles and simultaneously emits an angle position signal to the evaluation circuit that is representative for the instantaneous angle position. The evaluation circuit uses the distance signal and the angle position signal to determine the location of the object within the measuring range.
The quantity of the distance values obtained in a plane over a semicircle is hereunder referred to as "measurement fan".
The examples cited show that it is not possible to measure three-dimensional spaces rationally and with sufficient accuracy, as for instance required for measuring up operations, and true to deformation by applying sophisticated equipment and techniques, such as digital cameras or laser technique. In case of larger three-dimensional objects it is not possible to edit exact measurement values in the office in the sense of an integrated data system in such a way that thus all dimensions of a three-dimensional object are available for further processing. As explained earlier, also the evaluation of digitised photos (which can only be partially automated) is not a fundamental simplification of the measurement of such objects.
In accordance with DE 42 10 245 C2 a topographic recording system for an aerodynamic vehicle in order to scan the terrain is described. This is a topographic measurement method that requires the absolute coordinates to evaluate the measured data. The former are made available by GPS systems and INS (inertial navigation system) with which aircraft are equipped. As the prior state of the art, the above-mentioned DE 42 10 245 C2 states that by seeking homologous picture elements in a downstream signal preparation stage it is thus possible to use the picture signals to calculate the flight orientation data required for the evaluation in all six degrees of freedom and to create either stereoscopic image strips or a three-dimensional model of the overflown terrain in a digitised format. The further development of the prior state of the art by the invention in accordance with DE 42 10 245 C2 the absolute coordinates are still necessary. The seeking of homologous picture elements for the calculation of stereoscopic image strips is carried out with a linear-array camera and a distance sensor with a downstream signal processing stage. The correlation of homologous picture elements, however, requires very extensive calculation efforts and proposals are put forward as to how to remedy this situation. The topographic recording system takes measurements in parallel strips in this method, which in no case it suited for 3 D interior space visualisation and surveying.